Apparatus for the X-ray analysis of a liquid suspension of specimen material



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COHEN ETAL 3,246,146

APPARATUS FOR 'iI-IE XRAY ANALYSIS OF A LIQUID SUSPENSION OF SPECIMEN MATERIAL Filed July 11 1963 2 Sheets-Sheet l Apnfi 32, 1956 E. COHEN ETAL APPARATUS FOR THE XRAY ANALYSIS OF A LIQUID SUSPENSION OF SPECIMEN MATERIAL 2 Sheets-Sheet 2 Filed July 11, 1963 United States Patent 3,246,146 APPARATUS FOR THE X-RAY ANALYSIS OF A LIQUID SUSPENSION 0F SPECIMEN MATERIAL Enrico Cohen, Northwood, and Roy Witty, Hale, England,

assignors to Associated Electrical Industries Limited,

London, England, a British company Filed July 11, 1963, Ser. No. 294,310 3 Claims. (Cl. 250-49.5)

It is well known that characteristic X-radiations are emitted when a beam of electrons strike a suitable target. 'It is also well known that the wavelengths of these radiations can be determined, for instance by means of a spectrometer fitted with a suitable crystal. Hence if a metal body whose composition is to be determined is made the target of a demounta-ble X-ray tube, it is possible to determine the wavelengths of the various components of the emitted radiation, and thus obtain an analysis of the elements of which the metal body is composed. By the use of a suitable detector it is possible to obtain a quantitive analysis.

Although the above method of determining composition by X-r-adiation analysis can be very sensitive, it has the disadvantage that the material of a specimen to be analysed must be formed into a body of suitable shape and dimensions to constitute the tar-get of the X-ray tube, a requirement which may be inconvenient or impossible. To avoid the difiioulty, another method is often used in which the specimen is irradiated with X-rays from either a demountable or a sealed-off X-ray tube and the characteristic fluorescent radiation produced by the specimen is then analysed. With this latter method it is possible to have solid, powdered or liquid specimens, but the sensitivity of this method is much lower than that of the direct emission method, largely because the X-rays have to traverse a path of significant length before reaching the specimen.

In certain classes of work, the specimen is in, or can be converted to, the form of a liquid suspension or slurry of the specimen material. According to the invention there is provided in one aspect thereof a method of determining the composition of a specimen by X-radiation analysis, in which a liquid suspension of the specimen material is introduced into a cell aranged to constitute with said suspension a composite X-ray tube target such that on energization of the X-ray tube the specimen material in the cell will be excited to emit characteristic X- radiation, said radiation being analysed as before to obtain an analysis of the specimen.

The invention also provides, in another aspect, an X- ray tube target comprising a hollow cell into which a liquid suspension of specimen material to be analysed can be introduced and which constitutes with such suspension, a composite X-ray tube target from which can be obtained, by subjection thereof to the electron emission of an X-ray tube, X-radiation characteristic of the specimen.

The target cell may include an entry window through which the electron emission of the X-ray tube can enter the cell so as to excite the specimen material and cause it to emit its characteristic radiation. Alternatively such entry window may be provided, on its surface external to the cell (namely the surface on which the electron emission will impinge), with a layer of target material such as will produce on subjection to the electron emission X- rays which by entering the cell through the window will excite the specimen material to produce its characteristic radiation. (It will be appreciated that in this second alternative the target material must be so chosen that its own characteristic radiation will not mask that of the specimen.) The second alternative is preferred because windows which will pass X-rays without substantial ab- 3,246,146 Patented Apr. 12, 1966 sor-ption are easier to provide than are windows which will pass electrons. Thus, for example, a beryllium or aluminum window which will pass X-rays with relatively little absorption may absorb electrons to a significant extent. The characteristic radiation emitted by the specimen may be arranged to enter a spectrometer or other radiation analysing apparatus by passing out of the cell through the same window. However, particularly when the entry window has a layer of target material as aforesaid (which layer would tend to absorb characteristic radiation passing back through this window), it is preferred to provide in the opposite side of the cell a separate exit window for the characteristic radiation. This exit window again may be of beryllium or aluminum. Other materials which may be used for the window or windows are certain plastics materials able to be produced in thin sheets, an example of this being the polyester film supplied under the trademark Melinex. However such materials tend in time to deteriorate or change in character when subjected to radiation, so that if they were used they may have to be periodically replaced.

In order that the invention may be more fully understood reference will now be made to the accompanying drawings in which:

FIG. 1 illustrates in schematic outline a form of apparatus permitting X-radiation analysis of a specimen in the form of a liquid suspension by the method of the present invention;

FIGS. 2, 3 and 4 are respectively an end view, a crosssectional side view taken on the line IIIIII in FIG. 2, and a cross-sectional plan view taken on the line IVIV in FIG. 2, of a target cell suitable for apparatus such as that of FIG. 1, FIGS. 3 and 4 also showing the manner in which the target cell may be mounted on the end of an X-ray tube;

FIG. 4a illustrates a modification for the entry window of the cell; and

FIGS. 5 and 6 illustrate arrangements for obtaining a flow of liquid suspension through the target cell.

Referring to FIG. 1, an X-ray tube 1 is schematically illustrated as comprising the usual filament 2 and cathode 3 by which, on the application of suitable electrical potentials, a high energy electron beam 4 is obtained and directed on to the X-r-ay tube target. In this case the target is constituted by a hollow target cell 5 having inlet and outlet connections 6 and 7 by which a liquid suspension of a specimen material to be analysed can be introduced into the cell. The cell 5 has an entry window 8 and an exit window 9. The entry window 8 may be made simply of a thin sheet of material which will pass electrons so that the electron beam 4 will excite the suspended specimen material within the cell and cause it to produce its characteristic radiation. However electrons would have a greater tendency to -be absorbed by the material of the window than would X-rays, with consequent reduction of sensitivity, and it is therefore preferred to provide at the surface of the window 8 nearer the cathode structure 23 a layer of a heavier target material which will produce primary X-rays on subjection to the electron beam 4. These primary X-rays will enter the cell 5 through the window 8 and will excite characteristic radiation from the specimen material in suspension. As previously mentioned the target material used for such layer on the window 8 would be so chosen that its own characteristic r radiation would not mask that of the specimen: for instance if one were particularly interested in detecting and determining zinc content of the specimen, gold would be a suitable target material.

Whatever the form of the entry window 8, the characteristic radiation emitted by the specimen material in suspension will leave the cell 5 through the exit window 9 and can be analysed in a suitable form of radiation analysing apparatus. It will be noticed that the liquid suspension will be in intimate contact with the insides of the windows 8 and 9 so that a minimum length of path has to be traversed by the X-radiations before they reach the outside of the cell. Moreover the arrangement can also permit the external ray paths to be reduced in length as compared with those present in previous apparatus serving the same function.

The analysing apparatus is illustrated by way of example as a spectrometer comprising a collimator 10, an analysing crystal 11 and a detector 12. Radiation of any particular wavelength will in known manner be reflected by the crystal only when the crystal has a particular orientation in relation to the incident direction of the radiation. Consequently, the wavelength spectrum of the radiation emitted by the specimen (which spectrum reveals the composition of the specimen) can be determined by rotating the crystal and the detector 12 and detecting the angular positions at which radiation reflection takes place. The detector 12 has to rotate through twice the angle of rotation of the crystal 11. If the detector is constituted by a radiation counter a quantitive analysis of the composition can be obtained. A monitor counter 13 may also be provided. Instead of a spectrometer other forms of analyser may be employed, such for example as a scintillation or proportional counter in conjunction with a pulse height analyser.

FIGS. 2-4 illustrate :by way of example a practical form of the target cell of FIG. 1. The cell comprises a plate 14 through wich is formed a circular hole 15 of stepped diameter. Discs 16 and 17 constituting the entry and exit windows of the target cell are spaced apart by a spacing ring 18 and with it are held in position within the hole 15 by means of a locking ring 19. The entry window 16 is shown as being provided with a continuous layer 16' of a heavier target metal such for example as gold, the thickness of this layer being so chosen that it will absorb substantially the whole of the incident electron emission while giving optimum excitation and transmission of its own X-rays. As an alternative the layer 16 may be discontinuous, being for instance in the form of a grid having either a parallel strip formation as shown in FIG. 4a or a lattice formation or being in the form of a pattern of spots of the target material, or being constituted by a diffusion of the target material into the window material. Diametrically opposed tapered openings 20 and 21 in the spacing ring 18 are alignedwith tapered slots 22 and 23 in the width of the plate 14 and in conjunction with these latter slots constitute inlet and outlet ports of venturi form extending into the space between the windows 16 and 17. The venturi formation will assist in minimising the production of eddies within the cell: this could also be achieved by designing the interior of the cell to present to the fluid flow a substantial constant cross-sectional area.

It is to be understood that in FIGS. 3 and 4 the thickness of the windows has been exaggerated, these windows being normally as thin as possible commensurate with adequate strength. Also in FIG. 4a the width of the grid strips and of the spaces between them have been exaggerated.

As shown in FIGS. 3 and 4 the target cell may be mounted on thevend of an X-ray tube 24 by means of screws or studs 25 screwed into a plate 26 of similar outline to the plate 14 welded round the end of the tube 25. The extreme end of the tube 24 is shown as projecting somewhat proud of the plate 26 so that it forms a locating spigot portion 27 which engages in a circular recess in the facing surface of the plate 14. The evacuated space within the tube 24 is' sealed at this end by means of O-ring seals 28.

The liquid suspension of specimen material to be analysed is preferably caused to flow through the target cell. For instance a small portion of a process flow can be diverted to flow through the cell as is illustrated in FIG. 5, in which a branch pipe 29 is shown leading off a main flow pipe 30 towards the target cell 5. In this way a sensibly continuous analysis can be obtained. If only small amounts are available for analysis the liquid suspension may be continuously circulated through the target cell in a closed circuit so as to give adequate sampling, this being illustrated in FIG. 6 in which a container 31 for the liquid suspension is shown connected to a pump 32 which circulates the liquid suspension through the target cell 5 back to the container 31.

Normally water is used to cool the target of an X-ray tube. In the present case, by causing the liquid suspension to flow through the target cell it can also act as the coolant, thereby eliminating the need for a separate cooling circuit. I

What we claim is:

1. X-rayanalysis apparatus comprising an'X-ray tube having means for producing an electron emission therein, a hollow cell located in the target position of said X-ray tube so as to be subjected to said emission and having an entry window facing the emission means and anX-ray exit window, means for introducing into the cell a liquid suspension of a specimen material to be analysed, said entry window being of an electron transparent material permitting passage of the electrons into the cell to excite characteristic X-radiation from the suspended specimen material within it, and X-radiation analyser positioned to receive and analyse the characteristic X-radiation issuing through said exit window from the suspended specimen material.

2. X-ray analysis apparatus comprising an X-ray tube having means for producing an electron emission therein, a hollow cell located in the target position of said X-ray tube so as to be subjected to said emission and having an entry window facing the emission means and an X-ray exit window, means for introducing into the cell a liquid suspension of a specimen material to be analysed, said entry window having on its outer surface a layer of target material capable of emitting primary X-rays on subjec- References Cited by the Examiner I UNITED STATES PATENTS 2,418,029 3/1947. Hillier 250-51.5 X

2,559,526 7/1951 Van de Graafi et al. 313--330 X 2,680,814 6/1954 Robinson 250--49.5

2,791,698 5/1957 Dyroff et al. 250-51.5 X

2,848,624 8/1958 Friedman et al. 250-515 X 3,031,571 4/1962 Fearon 25051.5 X

RALPH G. NILSON, Primary Examiner. 

1. X-RAY ANALYSIS APPARATUS COMPRISING AN X-RAY TUBE HAVING MEANS PRODUCING AN ELECTRON EMISSION THEREIN, A HOLLOW CELL LOCATED IN THE TARGET POSITION OF SAID X-RAY TUBE SO AS TO BE SUBJECTED TO SAID EMISSION AND HAVING AN ENTRY WINDOW FACING THE EMISSION MEANS AND AN X-RAY EXIT WINDOW, MEANS FOR INTRODUCING INTO THE CELL A LIQUID SUSPENSION OF A SPECIMEN MATERIAL TO BE ANALYSED, SAID ENTRY WINDOW BEING OF AN ELECTRON TRANSPARENT MATERIAL PERMITTING PASSAGE OF THE ELECTRONS INTO THE CELL TO EXCITE CHARACTERISTICS X-RADIATION FROM THE SUSPENDED SPECIMEN MATERIAL WITHIN IT, AND X-RADIATION ANALYSER POSITIONED TO RECEIVE AND ANALYSE THE CHARACTERISTICS X-RADIATION ISSUING THROUGH SAID EXIT WINDOW FROM THE SUSPENDED SPECIMEN MATERIAL. 